Many industrial operations require that a supply of liquid be evenly distributed into a continuous thin sheet which is deposited onto a surface. One such operation is found in the pulp and paper making industry, wherein a spray of liquid is used to wash chemicals through a pulp sheet. A vacuum is applied within a cylinder or drum upon which the pulp sheet is positioned to pull liquids or filtrate applied to the sheet through the sheet, thus washing or removing such chemicals.
In such an operation, a large rotary drum supported at its ends is commonly used. The drum is covered by a filter screen and the interior of the drum is exposed to a vacuum plenum. The drum is partially submerged into a pool of wood pulp, the wood pulp being dispersed in a pulp slurry or filtrate. As the drum rotates through the pool, wood pulp and pulp slurry are collected against the outer surfaces of the filter screen to form a wet mat of pulp fibers. As the filter screen emerges from the pool, the pulp slurry is drawn inwardly against the filter screen, and the chemical laden filtrate is drawn through the filter screen and is subsequently discharged through suitable piping.
The wet mat is preferably washed through one or more washing stages. Each stage is in continuous rotation. Washing is only performed during the wash cycle on each stage. There may be one or more showers used in the wash cycle. The fibers washed will only see the filtrate or wash water from each shower once during rotation on each drum. The chemicals which are used in the pulp slurry are recovered. The recovered chemicals may then be reprocessed and reused. Washing of the mat is achieved by directing a spray of water wash toward the wet pulp mat to displace the chemical-laden pulp slurry from the mat. The water wash should be applied gently to prevent damage to the mat. A thin spray or film of water is usually used. The water wash is commonly applied through multiple parallel shower pipes which are angularly spaced around a segment of the rotary drum. The shower pipes extend axially along the length of the drum and are supported at their ends. Usually, the shower pipers are placed from just above the surface of the pool inlet side to the top of the drum, proceeding in the direction of drum rotation. The shower pipes have similar lengths and are spaced a fixed distance from the filter screen so that spray intensity and distribution are substantially uniform across the width of the mat. Drum sizes may be different lengths, but showers on a given drum are the same length.
The following patents relate to devices used in the paper and pulp industry. A variety of different shower pipes have been developed in an attempt to evenly distribute such a water wash. Some shower pipes are designed with an exterior flange or spillway surface to direct a spray or film of water tangentially toward the moving pulp mat. LaValley (U.S. Pat. No. 4,522,716, issued June 11, 1985); Wilt et al. (U.S. Pat. No. 4,511,088, issued Apr. 16, 1985); and Schibbye (U.S. Pat. No. 3,032,100, issued May 1, 1962) disclose liquid distribution devices having curved exterior spillways. Schibbye ('100) also discloses the use of vertical guide vanes which are positioned parallel to the flow of water. Penrod et al. (U.S. Pat. No. 2,940,418, issued June 14, 1960) discloses an air doctor device used to discharge pressurized air through a slot for smoothing a fluid slurry coating material that has been applied to the surface of a paper web. Russell (U.S. Pat. No. 3,134,654, issued May 26, 1964) discloses a high velocity dryer tube arranged to discharge gases, such as steam or air.
Other liquid or gas discharge devices may be found in non-analogous art. For example, Fontaine (U.S. Pat. No. 4,535,936, issued Aug. 20, 1985) discloses an air blast nozzle, wherein air is blasted out through an elongated slot, for blowing liquids off of surfaces such as sheet metal. Nicholson (U.S. Pat. No. 4,435,891, issued Mar. 13, 1984) discloses a method of manufacturing a sanitary fan spray nozzle for use in the food industry and particularly for use within a cheese filter. Beall (U.S. Pat. No. 329,527, issued Nov. 3, 1885) discloses a burner for a gas-stove.
The shower pipe devices known in the prior art have only been partially successful in meeting the needs of the paper and pulp industry. The previously known devices tend to cause damage to the pulp mat and accompanying machinery and often do not provide an effective spray pattern.
For example, during the removal process of the washed pulp mat, some wood pulp often is ineffectively washed. Poor consistency upon startup because of fluctuations in the vacuum causes thick and thin spots in the pulp mat. The thick areas wedge under the shower pipes between the drum and the shower. This wedging effect in concert with the rotation of the drum produces the damaging effect further described below. More particularly, the pulp build-up can break the exterior flanges, spillways, or nozzles of the shower pipes. The previously known shower pipe devices are not designed to provide adequate resistance to fatigue or failure, as described above. Substantial damage and loss of operational time occurs when the shower pipes are incapacitated due to breakage or clogging. Such damage is particularly prevalent where the shower pipes are in close proximity to the outer surface of the pulp mat.
Another persistent problem is the tendency of the shower pipes to sag. Rotary drums often exceed twenty feet in length. This requires the shower pipes to be even longer if complete spray coverage is to be obtained. The shower pipes are usually supported at their ends, and sometimes have an intermediate support. During the washing procedure, the shower pipes are filled with water or another washing liquid. The combined weight of the shower pipe and the contained liquid often causes the pipes to sag. Sagging or deformation can also be caused by manloading during inspection or plant outage periods. Sagging causes the shower pipe to apply the liquid at different velocities and consistencies along the length of the drum. The result is a very ineffective spray pattern. Uniformity and thickness of the spray consequently suffers. Another result of a sagging shower pipe is the increased likelihood that damage will occur to either the mat or operating machinery. Damage is usually caused by the inadvertent contact between the mat, filter or drum, and the shower pipes.
The spray patterns of the previously known shower pipes have also been found to be inconsistent in uniformity and thickness across the width and length of the pulp mat. It is desirable to wash the pulp mat uniformly across its width using a continuous or overlapping spray which traverses the axial length of the drum. To achieve a proper spray, a single or double row of spray holes spaced along the length of the shower pipe have been used. An exterior continuous lip, flange, or spillway may also be positioned diagonally across the spray outlets or holes to cause the fluid being sprayed from the outlet to fan outwardly. The previously known designs have had only limited success in providing a uniform spray because eddies in the liquid flow cause a buildup of wash liquid to occur near the outlet opening or orifice and along the flange or spillway. The previously known spillways also tend to accumulate debris from the spray-back or accumulation of random pulp mat as a result of the washing process. Such debris tends to plug the spray outlets of the shower pipes and disrupts uniformity of spray patterns, thereby negatively affecting the spray configuration.
Citation of the above listed references do not constitute an admission that the references are relevant or material to the present claims. These references are cited only as constituting the closest art to the general field of disclosure of which the applicant and his attorneys are aware. None of the references incorporate the combination of features taught in the present invention, nor do the previously known devices impart the same degree of effectiveness or efficiency as found in the present invention.